The present invention relates to a print image treatment device used in a stencil printing device or the like. The present invention is effective as a measure particularly for a set-off and seeping-through in printing.
In printing using liquid printing ink, there have been problems: a set-off, a symptom that a printing ink forming a print image on a printed body sticks to the back surface of another placed thereon, when printed bodies are piled up immediately after printing; a print image deformation occurring when a finger slightly touches a print image surface immediately after printing; and a seeping-through, a symptom that a printing ink forming a print image on a printing body, such as a sheet and printing paper penetrates through the printing body to the back surface.
These problems as mentioned above are apt to appear particularly in a stencil printing which uses excessive quantity of printing ink, in forming a print image on a printing body compared to the other type of printing.
Efforts have been made to reduce an applied quantity of ink to a printing body on printing processes to prevent a set-off, seeping-through, or the like from occurring. However, it is difficult to quantitatively control ink; overcontrolling an applied quantity of ink will cause a print image to be thin or to blur, and will lower the printing quality.
To avoid problems as mentioned above, it is considered to heat and dry a printing ink forming a print image, but this method needs to use a heater having a considerably high power. When a drying means by a heater or the like dries a printing body, conditions imposed on the drying means are more strict as the printing speed of a printing machine gets higher. Practically, it is impossible to dry a printing ink in such a high speed as to prevent a set-off, seeping-through, or the like from occurring.
Furthermore, depending on a printing system, a fine powder such as starch or talc can be applied to a print image for preventing a set-off. However, such a device as to apply these fine powders uses compressed air; a printing device having this type of device is apt to be considerably large.
And, when a printing body is transferred to a discharge paper tray, sorter, or the like after printing, it is impossible to allow a transfer roller to touch a print image on the printing body to keep the print image in a good condition. Thus, a conveyer belt has been used to transfer the printing body by a transfer mechanism touching only with the back surface (non-printed surface) of the printed body. The printed body transfer device of this type has been disclosed in, for instance, Japanese Patent Laid Open No. 50-88769.
However, compared to a transfer system used in a PPC copy machine or the like that transfers a copying paper forcibly by nipping both sides, the system transferring a printing body without touching the print image surface, but touching the back surface only, creates irregularities in paper setting in a transferred place such as a discharged paper tray or sorter; consequently deteriorating the neatness of a discharged paper. This tendency is more obvious as a printing speed, in other words, a paper discharging speed becomes higher. And, these problems drastically reduce the degree of freedom for designing a paper carrying and discharging path in the printing device.